The ultimate goal of this research proposal is to define the role of EGFR, ErbB2, 110 kD-sEGFR and p105-sErbB2, individually or in combination, in the tumor biology of Hispanic women diagnosed with breast cancer. As a corollary, we are interested to elucidate if the biology of the tumor is responsible for the differences in breast cancer incidence, mortality and clinical outcome observed among women with different racial/ethnic backgrounds. As a first step toward this goal, we hypothesize that the expression of EGFR, ErbB2, p105-sErbB2, and 110 kD-sEGFR is altered in Hispanic women diagnosed with breast cancer. Therefore, we propose experiments to determine the expression of EGFR and ErbB2 in the tumors of Hispanic women with breast cancer. In addition, the serum levels of 110 kD-sEGFR and p105-sErbB2 will be determine in the same group of patients. The results of these experiments/analyses will be compared with the clinical, pathological, and biological characteristics of the tumor. To determine if serum 110 kD-sEGFR and p105-sErbB2 arise from the tumor, the tissue expression of 110 kD-EGFR and ErbB2 will be correlated with the serum levels of 110 kD sEGFR and p105-sErbB2, respectively. For this study, we will recruit 100 Hispanic women newly diagnosed with breast cancer from two different regions, Puerto Rico and Texas (mainly the greater Houston area). We will recruit from each site 25 patients with clinical stage III breast cancer. The results from the proposed studies will provide the foundation for future studies with a large number of patients and for a longer period of time to correlate these molecules with clinical outcome such as overall survival and recurrence of the disease in Hispanic women with breast cancer. We are enthusiastic about these proposed studies and their implications for the diagnosis and treatment of Hispanic women with breast cancer.